Process for charging a longitudinal section of a catalyst tube

ABSTRACT

A process for charging a longitudinal section of a catalyst tube with a homogeneous fixed catalyst bed section whose active composition is at least one multielement oxide or comprises elemental silver on an oxidic support body and whose geometric shaped catalyst bodies and shaped inert bodies have a specific inhomogeneity of their longest dimensions.

The present invention relates to a process for charging a longitudinalsection of a catalyst tube with a uniform fixed catalyst bed sectionwhose active composition is at least one multielement oxide whichcomprises

-   a) the elements Mo, Fe and Bi, or-   b) the elements Mo and V, or-   c) the element V and additionally P and/or Sb,    or whose active composition comprises elemental silver on an oxidic    support body, and which consists of a single (preferably    intrinsically homogenized) type S^(i) or of a homogenized mixture of    a plurality of mutually distinguishable types S^(i) of geometric    shaped catalyst bodies or of geometric shaped catalyst bodies and    geometric shaped inert bodies, where the median of the longest    dimensions L_(S) ^(i) of the geometric shaped bodies of one type    S^(i) has a value D_(S) ^(i).

It is common knowledge to perform heterogeneously catalyzed partial gasphase oxidations over the fixed catalyst bed disposed in the usuallyvertical tubes (the so-called catalyst tubes) of tube bundle reactors(reactors which have a bundle of catalyst tubes present in a reactionvessel).

In this document, a complete oxidation of an organic compound withmolecular oxygen is understood to mean that the organic compound isconverted under the reactive action of molecular oxygen such that all ofthe carbon present in the organic compound is converted to oxides ofcarbon and all of the hydrogen present in the organic compound to oxidesof hydrogen. All different exothermic reactions of an organic compoundunder the reactive action of molecular oxygen are summarized here aspartial oxidations of an organic compound.

In particular, in this document, partial oxidations shall be understoodto mean those exothermic reactions of organic compounds under thereactive action of molecular oxygen in which the organic compounds to beoxidized partially, after the reaction has ended, comprise at least oneoxygen atom more in chemically bound form than before the partialoxidation was performed.

The tube bundle reactors required for aforementioned heterogeneouslycatalyzed partial gas phase oxidations are likewise known (cf., forexample, DE-A 44 31 949, EP-A 700 714).

In these reactions, the reaction gas mixture is conducted through thefixed catalyst bed disposed in the catalyst tubes of the tube bundlereactor, and the reactants are converted over the catalyst surfaceduring the residence time of the reactants.

The reaction temperature in the catalyst tubes is controlled by, interalia, conducting a fluid heat carrier (a heat exchange medium) aroundthe catalyst tubes of the tube bundle which are accommodated in avessel, in order to remove energy from the reaction system. Heat carrierand reaction gas mixture may be conducted either in cocurrent or incountercurrent over the tube bundle reactor.

In addition to the possibility of conducting the heat exchange medium ina simple manner essentially immediately longitudinally to the catalysttubes, this longitudinal conduction can also be realized merely over theentire reaction vessel and a transverse flow can be superimposed on thislongitudinal flow within the reaction vessel by virtue of anarrangement, successive along the catalyst tubes, of deflecting diskswhich leave free passage cross sections, so as to result in a meanderingflow profile of the heat exchange medium in the longitudinal sectionthrough the tube bundle (cf., for example, DE-A 44 31 949, EP-A 700 714,DE-C 28 30 765, DE-A 22 01 528, DE-A 22 31 557 and DE-A 23 10 517).

If required, essentially spatially separate heat carriers can beconducted around the catalyst tubes along different tube sections.

The tube section over which the particular heat carrier extendstypically represents a single reaction zone. A variant of such multizonetube bundle reactors used with preference is the two-zone tube bundlereactor, as described, for example, by the documents DE-C 28 30 765,DE-C 25 13 405, U.S. Pat. No. 3,147,084, DE-A 22 01 528, EP-A 383224 andDE-A 29 03 582.

Suitable heat exchange media are, for example, melts of salts such aspotassium nitrate, potassium nitrite, sodium nitrite and/or sodiumnitrate, low-melting metals such as sodium, mercury and alloys ofdifferent metals, ionic liquids (in which at least one of the oppositelycharged ions comprises at least one carbon atom), but also conventionalliquids, for example water or high-boiling organic solvents (for examplemixtures of Diphyl® and dimethyl phthalate).

Typically, the catalyst tubes are manufactured from ferritic steel orfrom stainless steel and have a wall thickness of a few mm, for examplefrom 1 to 3 mm. Their internal diameter is usually a few cm, for examplefrom 10 to 50 mm, frequently from 20 to 30 mm. The tube length extendsnormally to a few meters (a typical catalyst tube length is in the rangefrom 1 to 8 m, frequently from 2 to 6 m, in many cases from 2 to 4 m).Appropriately from an application point of view, the number of catalysttubes (working tubes) accommodated in the vessel extends to at least1000, frequently at least 3000 or 5000 and in many cases to at least10000. Frequently, the number of catalyst tubes accommodated in thereaction vessel is from 15000 to 30000 or 40000 or 50000. Tube bundlereactors having a number of catalyst tubes above 50000 are usually theexception. Within the vessel, the catalyst tubes are normally arrangedin essentially homogeneous distribution, the distribution appropriatelybeing selected such that the distance of the central internal axes ofmutually adjacent catalyst tubes (the so-called catalyst tube pitch) isfrom 25 to 55 mm, frequently from 35 to 45 mm (cf., for example, EP-A468 290).

Normally, in each case at least some of the catalyst tubes (workingtubes) of a tube bundle reactor, appropriately from an application pointof view their entirety, are manufactured homogeneously within the scopeof the manufacturing means. In other words, their internal diameter,their wall thickness and their tube length are identical within narrowtolerances (cf. WO 03/059857).

The aforementioned requirement profile also frequently applies to thefilling of such homogeneously manufactured catalyst tubes with shapedcatalyst bodies (cf., for example, WO 03/057653), in order to ensure anoptimal and substantially disruption-free operation of the tube bundlereactor. Especially for an optimal yield and selectivity of thereactions performed in the tube bundle reactor, it is essential thatpreferably all working tubes of the reaction are filled, i.e. charged,in a substantially uniform manner with the fixed catalyst bed.

Working tubes are typically distinguished from thermal tubes, asdescribed, for example, by EP-A 873 783. While the working tubes arethose catalyst tubes in which the chemical reaction to be performed isperformed in the actual sense, thermal tubes primarily serve the purposeof monitoring and of controlling the reaction temperature in thecatalyst tubes. For this purpose, the thermal tubes normally comprise,in addition to the fixed catalyst bed, a thermowell conducted centrallyalong the thermal tube and provided with a temperature sensor. Ingeneral, the number of thermal tubes in a tube bundle reactor is verymuch smaller than the number of working tubes. Normally, the number ofthermal tubes is ≦20.

Examples of heterogeneously catalyzed partial oxidations of organiccompounds include the conversion of propene to acrolein and/or acrylicacid (cf., for example, DE-A 23 51 151), the conversion of tert-butanol,isobutene, isobutane, isobutyraldehyde or the methyl ether oftert-butanol to methacrolein and/or methacrylic acid (cf., for example,DE-A 25 26 238, EP-A 92 097, EP-A 58 927, DE-A 41 32 263, DE-A 41 32 684and DE-A 40 22 212), the conversion of acrolein to acrylic acid, theconversion of methacrolein to methacrylic acid (cf., for example, DE-A25 26 238), the conversion of o-xylene or naphthalene to phthalicanhydride (cf., for example, EP-A 522 871) and the conversion ofbutadiene to maleic anhydride (cf., for example, DE-A 21 06 796 and DE-A16 24 921), the conversion of n-butane to maleic anhydride (cf., forexample, GB-A 1 464 198 and GB-A 1 291 354), the conversion of indanesto, for example, anthraquinone (cf., for example, DE-A 20 25 430), theconversion of ethylene to ethylene oxide or of propylene to propyleneoxide (cf., for example, DE-B 12 54 137, DE-A 21 59 346, EP-A 372 972,WO 89/0710, DE-A 43 11 608), the conversion of propylene and/or acroleinto acrylonitrile (cf., for example, DE-A 23 51 151), the conversion ofisobutene and/or methacrolein to methacrylonitrile (i.e. the term“partial oxidation” in this document shall also comprise partialammoxidation, i.e. a partial oxidation in the presence of ammonia), theoxidative dehydrogenation of hydrocarbons (cf., for example, DE-A 23 51151), the conversion of propane to acrylonitrile or to acrolein and/oracrylic acid (cf., for example, DE-A 101 31 297, EP-A 1 09 0684, EP-A608 838, DE-A 100 46 672, EP-A 529 853, WO 01/96270 and DE-A 100 28582), etc.

The active compositions of the catalysts to be used for the performanceof exothermic heterogeneously catalyzed partial gas phase oxidations oforganic compounds are generally at least one multielement oxide whichcomprises

-   a) the elements Mo, Fe and Bi, or-   b) the elements Mo and V, or-   c) the element V and additionally P and/or Sb,    or systems which comprise elemental silver on an oxidic support.

These active compositions are shaped to shaped bodies of a wide varietyof different geometries (to so-called geometric shaped catalyst bodies),in order to establish the fixed catalyst bed in the tubes of the tubebundle reactors (to charge the catalyst tubes with the fixed catalystbed). For example, useful such geometric shaped bodies include spheres,tablets, extrudates, rings, spirals, pyramids, cylinders, prisms,cuboids, cubes, etc.

In the simplest case, the geometric shaped body may consist only ofcatalytically active composition which may, if appropriate, be dilutedwith inert material. Such geometric shaped catalyst bodies are typicallyreferred to as unsupported catalysts.

In the case of unsupported catalysts, the shaping can be effected, forexample, by compacting catalytically active powder composition (forexample a pulverulent multielement oxide active composition) to thedesired catalyst geometry (for example by tableting, sintering orextruding). It is possible to add shaping assistants. Alternatively, apulverulent precursor composition can be compacted to the desiredcatalyst geometry and the resulting geometric shaped body can beconverted by thermal treatment (if appropriate in a molecularoxygen-comprising atmosphere) to the catalytically active shapedmultielement oxide body (cf., for example, US 2005/0263926).

It will be appreciated that the shaping can also be effected by coatinga geometric shaped body composed of catalytically inactive material (ofinert material) with active composition (also referred to hereinafter as“shaped support body” or, for short, as “support body”). Alternatively,it is also possible to coat with precursor composition and to effect theconversion to the active catalyst by subsequent thermal treatment (ifappropriate in a molecular oxygen-comprising atmosphere). The coatingcan be effected in the simplest manner, for example, by moistening thesurface of an inert support body by means of a liquid binder andsubsequently adhering pulverulent active composition or pulverulentprecursor composition on the moistened surface. The catalysts obtainablein this way are referred to as coated catalysts.

Suitable inert support bodies for many heterogeneously catalyzed partialgas phase oxidations are porous or nonporous aluminum oxides, siliconoxide, thorium dioxide, zirconium oxide, silicon carbide or silicatessuch as magnesium silicate or aluminum silicate (for example C220steatite from CeramTec), but also metals, for example stainless steel oraluminum (cf., for example, US 2006/0205978).

Instead of coating the inert (inert generally means that, when thereaction gas mixture is conducted through a catalyst tube charged onlywith inert support bodies under the reaction conditions, the conversionof the reactants is ≦5 mol %, usually ≦2 mol %) support bodies withpulverulent active composition or with pulverulent precursorcomposition, the support body can in many cases also be impregnated witha solution of the catalytically active substance or with a solution of aprecursor substance and the solvent can subsequently be volatilized and,if appropriate, a chemical reduction and/or thermal treatment (ifappropriate in an atmosphere comprising molecular oxygen) can follow.The geometric shaped catalyst bodies which result in this way aretypically referred to as supported or impregnated catalysts.

The longest dimension L of such geometric shaped catalyst bodies (as isquite generally the case for geometric shaped bodies in this document)is understood to mean the longest possible direct line connecting twopoints on the surface of the shaped catalyst body. It is (in geometricshaped inert bodies too) usually from 1 to 20 mm, often from 2 to 15 mmand in many cases from 3 or 4 to 10 or to 8 or to 6 mm. In the case ofrings, the wall thickness is additionally typically from 0.5 to 6 mm,frequently from 1 to 4 or to 3 or to 2 mm.

The fixed catalyst bed does not consist of a bed of a single type ofgeometric shaped catalyst bodies which is uniform along the individualcatalyst tube in all heterogeneously catalyzed partial gas phaseoxidations over the fixed catalyst bed present in the tubes of tubebundle reactors. Instead, the fixed catalyst bed may also consist of ahomogenized mixture of a plurality of (i.e. at least two) mutuallydistinguishable types S^(i) of geometric shaped catalyst bodies or ofgeometric shaped catalyst bodies and geometric shaped inert bodies overthe total length of the catalyst tube (i.e. such a mixture may consistof at least two mutually distinguishable types of geometric shapedcatalyst bodies, or of a single type of geometric shaped catalyst bodiesand of a single type of geometric shaped inert bodies, or at least twotypes of mutually distinguishable geometric shaped catalyst bodies andof a single type of geometric shaped inert bodies, or of at least twotypes of mutually distinguishable geometric shaped catalyst bodies andat least two types of mutually distinguishable geometric shaped inertbodies). Possible distinguishing features of the mutually differenttypes S^(i) are the type of geometry, the type of active composition,the type of support material, etc. Useful materials for the geometricshaped inert bodies include the same materials as have already beenrecommended for the inert geometric shaped support bodies in the coatedcatalysts and essentially do not intervene in the course of the gasphase partial oxidation. In principle, all inert shaped support bodiesare also useful as geometric shaped inert bodies for diluting geometricshaped catalyst bodies in a fixed catalyst bed. Such a dilution allowsthe volume-specific activity of a fixed catalyst bed to be adjustedspecifically to the requirement of the particular heterogeneouslycatalyzed partial gas phase oxidation.

The wording “homogenized mixture” means that measures have been taken inorder to mix the mutually different types of geometric shaped bodies (orthe different longest dimensions within one type) homogeneously with oneanother. Ideally, the homogeneous mixing along the entire longitudinalsection achieves the statistical average, also with regard to theparticular individual type.

In many cases, a catalyst tube charge (a catalyst tube filling) with afixed catalyst bed, though, also consists of a plurality of mutuallydistinguishable longitudinal sections ((longitudinal) fixed catalyst bedsections, catalyst bed sections) which are mounted one on top of another(in succession). Each individual longitudinal section can be configuredhomogeneously over its length as has already been explained for acatalyst tube charged uniformly over its total catalyst tube length. Atthe transition from an intrinsically homogeneous bed section to the nextintrinsically homogeneous bed section, the configuration (composition)of the bed changes abruptly. Thus, fixed catalyst beds which have aheterogeneous structure form along an individual catalyst tube. This isalso referred to as a structured filling (or bed) of the catalyst tubes.At the start (viewed in flow direction of the reaction gas flowingthrough the catalyst tube) and/or at the end of the catalyst tube, thefixed catalyst bed is frequently concluded by an exclusive bed ofgeometric shaped inert bodies.

Examples of such structured fillings of catalyst tubes are described,inter alia, in the documents US 2006/0161019, EP-A 979 813, EP-A 090744, EP-A 456 837, EP-A 1 106 598, U.S. Pat. No. 5,198,581 and U.S. Pat.No. 4,203,903.

In general, the filling of a catalyst tube with a structured fixedcatalyst bed is configured such that the volume-specific activity of thefixed catalyst bed increases in flow direction of the fixed catalystbed. The volume-specific activity of an intrinsically homogeneouslongitudinal section of a fixed catalyst bed charge of a catalyst tubeis increased when, with continuing charge of the catalyst tube as in thecorresponding longitudinal section of the catalyst tube under otherwiseidentical reaction conditions (i.e. identical composition of thereactions gas mixture, identical loading of the fixed catalyst bedcharge with reaction gas mixture and identical entrance temperature ofthe heat carrier and identical flow conditions of the heat carrier), anincreased reactant conversion results (based on single pass of thereaction gas mixture through the catalyst tube).

The loading of a fixed catalyst bed catalyzing a reaction step withreaction gas or with a reaction gas component is understood to mean theamount of reaction gas or of reaction gas component in standard liters(=I (STP); the volume in liters that the corresponding amount ofreaction gas or reaction gas component would take up under standardconditions, i.e. at 25° C. and 1 bar) which is conducted through oneliter of fixed catalyst bed per hour. Pure inert material bed sectionsare not included.

According to the teaching of the prior art, the geometric dimensions ofone type of geometric shaped catalyst bodies or of one type of geometricshaped inert bodies which are used to charge a longitudinal section of acatalyst tube with a homogeneous fixed catalyst bed for aheterogeneously catalyzed partial gas phase oxidation of an organiccompound should be substantially uniform within the particular type (cf.US 2006/0205978 and WO 2005/113123).

However, in-house investigations have shown that a defined inhomogeneityof the aforementioned dimensions has an advantageous effect on theselectivity of the target product formation.

Accordingly, the present invention provides a process for charging alongitudinal section of a catalyst tube with a uniform fixed catalystbed section whose active composition is at least one multielement oxidewhich comprises

-   a) the elements Mo, Fe and Bi, or-   b) the elements Mo and V, or-   c) the element V and additionally P and/or Sb,    or whose active composition comprises elemental silver on an oxidic    support body, and which consists of a single (preferably    intrinsically homogenized, i.e. essentially randomly distributed)    type S^(i) or of a homogenized mixture of a plurality of mutually    distinguishable types S^(i) of geometric shaped catalyst bodies or    of geometric shaped catalyst bodies and geometric shaped inert    bodies, where the median of the longest dimensions L_(S) ^(i) of the    geometric shaped bodies of one type S^(i) has a value D_(S) ^(i),    wherein, at least within one type S^(i) of geometric shaped bodies,    the proviso M that

from 40 of the total number of geometric shaped bodies belonging toS^(i) to 70% has a longest dimension L_(S) ^(i) for which 0.98 · D_(S)^(i) ≦ L_(S) ^(i) ≦ 1.02 · D_(S) ^(i), at least of the total number ofthe geometric shaped bodies belonging to 10% S^(i) has a longestdimension L_(S) ^(i) for which 0.94 · D_(S) ^(i) ≦ L_(S) ^(i) < 0.98 ·D_(S) ^(i), at least of the total number of the geometric shaped bodiesbelonging to 10% S^(i) has a longest dimension L_(S) ^(i) for which 1.02· D_(S) ^(i) < L_(S) ^(i) ≦ 1.10 · D_(S) ^(i), less of the total numberof geometric shaped bodies belonging to S^(i) than 5% has a longestdimension L_(S) ^(i) for which 0.94 · D_(S) ^(i) > L_(S) ^(i), and lessof the total number of the geometric shaped bodies belonging to than 5%S^(i) has a longest dimension L_(S) ^(i) for which 1.10 · D_(S) ^(i) <L_(S) ^(i)is satisfied.

Preferably in accordance with the invention, less than 3% of the totalnumber of the geometric shaped bodies belonging to S^(i) has a longestdimension L_(S) ^(i) for which 0.94·D_(S) ^(i)>L_(S) ^(i).

Moreover, preferably in accordance with the invention, less than 3% ofthe total number of the geometric shaped bodies belonging to S^(i) has alongest dimension L_(S) ^(i) for which 1.10·D_(S) ^(i)>L_(S) ^(i).

Very particularly preferably in accordance with the invention, less than1% of the total number of the geometric shaped bodies belonging to S^(i)has a longest dimension L_(S) ^(i) for which 0.94·D_(S) ^(i)>L_(S) ^(i).

Moreover, very particularly preferably in accordance with the invention,less than 1% of the total number of the geometric shaped bodiesbelonging to S^(i) has a longest dimension L_(S) ^(i) for which1.10·D_(S) ^(i)>L_(S) ^(i).

Advantageously, the aforementioned conditions (provisos) are satisfiedfor the majority and particularly advantageously for each of thedifferent types S^(i) within the fixed catalyst bed section.

Particularly advantageously, in the process according to the invention,at least within one type S^(i) of geometric shaped bodies of the fixedcatalyst bed section, the proviso M* that

from 50 (preferably 55%) of the total number of geometric shaped bodiesto 60% belonging to S^(i) has a longest dimension L_(S) ^(i) for which0.98 · D_(S) ^(i) ≦ L_(S) ^(i) ≦ 1.02 · D_(S) ^(i), at least of thetotal number of the geometric shaped bodies belonging to 15% S^(i) has alongest dimension L_(S) ^(i) for which 0.94 · D_(S) ^(i) ≦ L_(S) ^(i) <0.98 · D_(S) ^(i), at least of the total number of the geometric shapedbodies belonging to 15% S^(i) has a longest dimension L_(S) ^(i) forwhich 1.02 · D_(S) ^(i) < L_(S) ^(i) ≦ 1.10 · D_(S) ^(i), less of thetotal number of geometric shaped bodies belonging to S^(i) than 5% has alongest dimension L_(S) ^(i) for which 0.94 · D_(S) ^(i) > L_(S) ^(i),and less of the total number of the geometric shaped bodies belonging tothan 5% S^(i) has a longest dimension L_(S) ^(i) for which 1.10 · D_(S)^(i) < L_(S) ^(i)is satisfied.

Preferably in accordance with the invention, within the aforementionedframework, less than 3% of the total number of the geometric shapedbodies belonging to S^(i) has a longest dimension L_(S) ^(i) for which0.94·D_(S) ^(i)>L_(S) ^(i).

Moreover, within the aforementioned framework, advantageously less than3% of the total number of the geometric shaped bodies belonging to S^(i)has a longest dimension L_(S) ^(i) for which 1.10·D_(S) ^(i)>L_(S) ^(i).

Most preferably in accordance with the invention, within theaforementioned framework, less than 1% of the total number of thegeometric shaped bodies belonging to S^(i) has a longest dimension L_(S)^(i) for which 0.94·D_(S) ^(i)>L_(S) ^(i).

Moreover, within the aforementioned framework, preferably less than 1%of the total number of the geometric shaped bodies belonging to S^(i)has a longest dimension L_(S) ^(i) for which 1.10·D_(S) ^(i)>L_(S) ^(i).

Advantageously, the aforementioned framework conditions (provisos) aresatisfied for the majority and particularly advantageously for each ofthe different types S^(i) within the fixed catalyst bed section.

Very particularly advantageously, in the process according to theinvention, at least within one type S^(i) of geometric shaped bodies ofthe fixed catalyst bed section, the proviso M** that

from 50 (preferably 55%) of the total number of geometric shaped bodiesto 60% belonging to S^(i) has a longest dimension L_(S) ^(i) for which0.98 · D_(S) ^(i) ≦ L_(S) ^(i) ≦ 1.02 · D_(S) ^(i), at least of thetotal number of the geometric shaped bodies belonging to 20% S^(i) has alongest dimension L_(S) ^(i) for which 0.94 · D_(S) ^(i) ≦ L_(S) ^(i) <0.98 · D_(S) ^(i), at least of the total number of the geometric shapedbodies belonging to 20% S^(i) has a longest dimension L_(S) ^(i) forwhich 1.02 · D_(S) ^(i) < L_(S) ^(i) ≦ 1.10 · D_(S) ^(i), less of thetotal number of geometric shaped bodies belonging to S^(i) than 5% has alongest dimension L_(S) ^(i) for which 0.94 · D_(S) ^(i) > L_(S) ^(i),and less of the total number of the geometric shaped bodies belonging tothan 5% S^(i) has a longest dimension L_(S) ^(i) for which 1.10 · D_(S)^(i) < L_(S) ^(i)is satisfied.

Preferably in accordance with the invention, within the aforementionedframework, less than 3% of the total number of the geometric shapedbodies belonging to S^(i) has a longest dimension L_(S) ^(i) for which0.94·D_(S) ^(i).

Moreover, within the aforementioned framework, advantageously, less than3% of the total number of the geometric shaped bodies belonging to S^(i)has a longest dimension L_(S) ^(i) for which 1.10·D_(S) ^(i)>L_(S) ^(i).

Most preferably in accordance with the invention, within theaforementioned framework, less than 1% of the total number of thegeometric shaped bodies belonging to S^(i) has a longest dimension L_(S)^(i) for which 0.94·D_(S) ^(i)>L_(S) ^(i).

Moreover, within the aforementioned framework, preferably less than 1%of the total number of the geometric shaped bodies belonging to S^(i)has a longest dimension L_(S) ^(i) for which 1.10·D_(S) ^(i)>L_(S) ^(i).

Advantageously, the aforementioned framework conditions (provisos) areeach satisfied for the majority and particularly advantageously for eachof the different types S^(i) within the fixed catalyst bed section.

Moreover, for all frameworks detailed in this document, it isparticularly advantageous when no geometric shaped bodies belonging toS^(i) have a longest dimension L_(S) ^(i) for which 0.94·D_(S)^(i)>L_(S) ^(i).

Moreover, for all frameworks detailed in this document, it isparticularly advantageous when no geometric shaped bodies belonging toS^(i) have a longest dimension L_(S) ^(i) for which 1.10·D_(S)^(i)>L_(S) ^(i).

The median D_(S) ^(i) of the longest dimensions L_(S) ^(i) of thegeometric shaped bodies of one type S^(i) is defined such that 50% ofall (of the) longest dimensions L_(S) ^(i) of the geometric shapedbodies of one type S^(i) are less than or equal to D_(S) ^(i) (where themedian, unless explicitly stated otherwise in this document, is alwaysformed using the particular shaped bodies present in a homogeneouslycharged longitudinal section of the catalyst tube).

In principle, a uniformly charged longitudinal section of the catalysttube in the process according to the invention can extend over theentire catalyst tube length.

It will be appreciated that the entire fixed catalyst bed present in thecatalyst tube may also consist of a plurality of mutuallydistinguishable (each intrinsically homogeneously charged) fixedcatalyst bed sections (longitudinal sections). In this case, it isadvantageous when the process according to the invention is applied tothe majority, and particularly advantageous when it is applied to eachof the different fixed catalyst bed sections.

When the fixed catalyst bed in a catalyst tube also has longitudinalsections which consist exclusively of geometric shaped inert bodies, itis advantageous when the inventive procedure is also applied to thoseinert sections (these too satisfy the inventive provisos). However, theapplication of the inventive procedure to such inert sections is lessrelevant than in the case of catalytically active sections (in eachcase, these comprise catalytically active geometric shaped catalystbodies).

Inert sections may be used, for example, within a catalyst tube toseparate catalytically active sections spatially from one another.

In the simplest case, which is preferred from an application point ofview, mutually different, but in each case intrinsically homogeneous,fixed catalyst bed (longitudinal) sections (especially the catalyticallyactive sections) of a catalyst tube may differ (at least in as far asthey catalyze the same reaction step) only by virtue of a single type ofgeometric shaped catalyst bodies comprising active composition beingdiluted with a different proportion of a single type of inert geometricshaped inert bodies not comprising any active composition (in thesimplest case, these may, as already stated, be inert (shaped) supportbodies; but they may also be shaped inert bodies consisting of metal(for example stainless steel)) (in homogenized form). Advantageously,all fixed catalyst bed (longitudinal) sections of a catalyst tubecharged with a fixed catalyst bed for a heterogeneously catalyzedpartial gas phase oxidation differ exclusively in the aforementionedmanner (in this case, the fixed catalyst bed longitudinal sectioncharged only with the one type of geometric shaped catalyst bodies andthe fixed catalyst bed longitudinal section charged only with the onetype of geometric shaped inert bodies form the two possible dilutionboundary cases). Pure inert beds may also consist of a separate type ofshaped inert bodies.

In principle, within the context of the statements above, the one typeof inert shaped diluent bodies (shaped inert bodies) may have either thesame geometry as (which is preferred) or a different geometry from theone type of catalytically active shaped catalyst bodies.

When a single inventive fixed catalyst bed section consists of a(homogenized) mixture of only one type of geometric shaped catalystbodies and only one type of geometric shaped inert bodies, it isadvantageous in accordance with the invention (especially in the case ofthe same geometries of the two shaped body types) when the medianD_(cat) of the longest dimensions of the only one type of geometricshaped catalyst bodies and the median D_(inert) of the only one type ofgeometric shaped inert bodies (formed over the fixed catalyst bedsection) are of similar size. It is advantageous from an applicationpoint of view when 0.90≦D_(cat)/D_(inert)≦1.10. Very particularlyadvantageously from an application point of view, for the ratio of thetwo medians, 0.95≦D_(cat)/D_(inert)≦1.05. It is best when0.98≦D_(cat)/D_(inert)≦1.02, or D_(cat)/D_(inert)=1. TheD_(cat)/D_(inert) ratio shall hereinafter be abbreviated to V.

When all catalytically active fixed catalyst bed (longitudinal) sectionsof a fixed catalyst bed charge of a catalyst tube consist of different(homogenized) degrees of dilution (mixtures) of a single type ofgeometric shaped catalyst bodies with a single type of geometric shapedinert bodies (at least in as far as they catalyze the same reactionstep), the aforementioned ratios are, appropriately from an applicationpoint of view, intrinsically satisfied in each individual catalyticallyactive fixed catalyst bed (longitudinal) section having such a dilution(the two shaped body types preferably have the same geometry).

Very particularly appropriately from an application point of view(especially when the two shaped body types have the same geometry), themedian ratio is within one of the aforementioned ranges when the medianis formed over the entire catalytically active fixed catalyst beddisposed within the catalyst tube (or over all fixed catalyst bed(longitudinal) sections which catalyze the same reaction step) (evenbetter, the median ratio is within one of the aforementioned ranges whenpure inert beds are also included in the median formation over theentire fixed bed present in the catalyst tube).

A series arrangement of such fixed catalyst bed (longitudinal) sectionshaving a different degree of dilution (formed from only one type ofgeometric shaped inert bodies and only one type of geometric shapedcatalyst bodies) can generate, in each case adapted specifically to therequirements of the heterogeneously catalyzed partial gas phaseoxidation to be performed, along a catalyst tube, dilution profiles(dilution structures) of a wide variety of different types, the twoshaped body types, advantageously from an application point of view,having the same geometry. In many cases, the dilution structure isselected such that the degree of dilution decreases in flow direction ofthe reaction gas mixture (i.e. the volume-specific active compositionincreases in flow direction; wherever the reactant concentration ishigh, the volume-specific activity is low and vice versa). If required,the dilution profile (the activity structuring) can, though, be selectedconversely or completely differently.

As already mentioned, preferably all catalytically active (in each case,they comprise geometric shaped catalyst bodies) fixed catalyst bed(longitudinal) sections of a fixed catalyst bed charge of a catalysttube (at least in as far as they catalyze the same reaction step)consist of different (homogenized) degrees of dilution (mixtures) of asingle type of geometric shaped catalyst bodies with a single type ofgeometric shaped inert bodies (including the “0” degree of dilution;such a catalytically active fixed catalyst bed (longitudinal) sectionconsists exclusively of the one type of geometric shaped catalystbodies).

When the one type of geometric shaped catalyst bodies and the one typeof geometric shaped inert bodies advantageously, in addition, have thesame geometry and a combined median D^(inert) _(cat) is formed over all(over the total number G of) longest dimensions L_(cat) and L_(inert) ofthe geometric shaped catalyst bodies and of the geometric shaped inertbodies which are present in the entirety of these fixed catalyst bed(longitudinal) sections, it is advantageous in accordance with theinvention when the proviso M^(G) that

from 40 (preferably from 50 to 60) % of the total number G of geometricto 70 shaped catalyst bodies and geometric shaped inert bodies has alongest dimension L_(cat,inert) for which 0.98 · D^(inert) _(cat) ≦L_(cat,inert) ≦ 1.02 · D^(inert) _(cat), at least (preferably 15 or 20)% of the total number G has a longest 10 dimension L_(cat,inert) forwhich 0.94 · D^(inert) _(cat) ≦ L_(cat,inert) < 0.98 · D^(inert) _(cat),at least (preferably 15 or 20) % of the total number G has a longest 10dimension L_(cat,inert) for which 1.02 · D^(inert) _(cat) <L_(cat,inert) ≦ 1.10 · D^(inert) _(cat), less (preferably less than 3 or1 (or 0%))% of the total number G than 5 has a longest dimensionL_(cat,inert) for which 0.94 · D^(inert) _(cat) > L_(cat,inert), andless (preferably less than 3 or 1 (or 0%))% of the total number G than 5has a longest dimension L_(cat,inert) for which 1.10 · D^(inert) _(cat)< L_(cat,inert).is satisfied.

However, it is also already advantageous when the proviso MG issatisfied only within a homogeneous fixed catalyst bed (longitudinal)section or at least formed over the majority of the fixed catalyst bed(longitudinal) sections.

Normally, within a catalyst tube, those fixed catalyst bed(longitudinal) sections which catalyze the same reaction step follow oneanother in succession in flow direction of the fixed catalyst bed.

When, within a catalyst tube, more (in the majority of cases, only onereaction step is catalyzed within a catalyst tube) than one reactionstep is catalyzed (for examples first the step from propylene toacrolein and, downstream thereof in flow direction, the step fromacrolein to acrylic acid), the fixed catalyst bed generally has a numberof aforementioned fixed catalyst bed (longitudinal) section sequencescorresponding to the number of reaction steps. When such a fixedcatalyst bed (longitudinal) section sequence begins or ends with a fixedbed section consisting only of shaped inert bodies, it is favorable inaccordance with the invention when these shaped inert bodies are of thesame type as those used in the downstream or upstream fixed catalyst bed(longitudinal) section sequence. Moreover, it is advantageous inaccordance with the invention when the aforementioned relationshipframework (the aforementioned provisos M^(G)) is also satisfied whensuch fixed bed sections consisting only of shaped inert bodies areincluded.

For the production of one type S^(i) of geometric shaped coated catalystbodies (shaped supported catalyst bodies) which satisfy the inventiverequirement profile, the starting point will generally be one type ofgeometric shaped support bodies which (viewed as one type of geometricshaped inert bodies) already as such satisfy the inventive requirementprofile, and these will be coated (or impregnated) uniformly with finelydivided active composition or with finely divided precursor compositionof the active composition by known prior art processes. For thispurpose, for example, the coating process described in US 2006/0205978can be employed. Alternatively, the coating process of EP-A 714 700 canbe employed.

In order to obtain one type of geometric shaped support bodies which,with regard to their longest dimensions, satisfy the inventiverequirement profile, it is possible in a simple manner to proceed fromgeometric shaped support body types for which, between the median oftheir longest dimensions D_(S)* and the accompanying longest dimensionsL_(S)*, the relationship B0.99·D _(S) *≦L _(S)*≦1.01·D _(S)*  (B)is satisfied.

Shaped support body types which are different from one another in themanner required may then be mixed homogeneously with one another(homogenized) in the required quantitative ratios. In a correspondingmanner, types S^(i) of geometric shaped inert bodies suitable inaccordance with the invention are obtainable.

For the production of one type S^(i) of geometric shaped unsupportedcatalyst bodies which satisfies the inventive requirement profile, it ispossible to proceed in a corresponding manner. In other words, forexample according to the procedure disclosed in US 2005/0263926, shapedunsupported catalyst body types (or shaped unsupported catalystprecursor body types which are yet to be calcined (to be treatedthermally)) which satisfy the relationship B are obtained. Appropriate(homogenizing) blending of such mutually different types subsequentlyallows, in accordance with the invention, required types S^(i) to beobtained.

Everything stated in this document applies especially when both thegeometric shaped catalyst body types and the geometric shaped inert bodytypes are rings (or spheres).

This is especially true when the active composition of such catalystrings is a multielement oxide of the general formula IMo₁₂Bi_(a)Fe_(b)X¹ _(c)X² _(d)X³ _(e)X⁴ _(f)O_(n)  (I)where

-   X¹=nickel and/or cobalt,-   X²=thallium, an alkali metal and/or an alkaline earth metal,-   X³=zinc, phosphorus, arsenic, boron, antimony, tin, cerium, lead,    vanadium, chromium and/or tungsten,-   X⁴=silicon, aluminum, titanium and/or zirconium,-   a=0.2 to 5,-   b=0.01 to 5,-   c=0 to 10,-   d=0 to 2,-   e=0 to 8,-   f=0 to 10, and-   n=a number which is determined by the valency and frequency of the    elements in I other than oxygen    (it will be appreciated that aforementioned multielement oxides I    may also be used as the active composition for all other possible    geometric shaped catalyst body types.)

Descriptions of the preparation of corresponding unsupported catalystrings and coated catalyst rings (or spheres in each case) can be found,for example, in WO 02/30569, in WO 2005/030393, in Research DisclosureRD 2005-497012, in DE-A 10 2007 005 602 and in DE-A 10 2007 004 961. Inthe aforementioned documents, those annular catalysts (and quitegenerally catalysts with a multielement oxide I as the activecomposition) whose active composition is a multielement oxide I arerecommended, especially for a heterogeneously catalyzed partialoxidation of propylene to acrolein or acrolein and acrylic acid, andalso of isobutene to methacrolein. The ring geometries recommended inthe aforementioned documents should be understood, in the context of thepresent invention, as median ring geometry of one type of annular shapedcatalyst bodies. In other words, the median of the internal ringdiameter, the median of the external ring diameter and the median of thering length of an annular shaped catalyst body type S^(i) to be used inaccordance with the invention may have the magnitudes specified in eachcase in the aforementioned documents.

The external diameter of these median ring geometries may be, forexample, from 2 to 10 mm, or from 2 to 8 mm, or from 4 to 8 mm (the sameapplies in the case of sphere geometries).

The length of these median ring geometries may likewise be, for example,from 2 to 10 mm, or from 2 to 8 mm, or from 4 to 8 mm. The median of thewall thickness of such ring geometries is appropriately generally from 1to 3 mm.

The median of the particular ring dimension (this is also true in thecase of all other ring geometries addressed in this document or otherring geometries (for example sphere geometry) of one type S^(i) ofshaped catalyst bodies in relation to the median of a specific dimensionof the particular geometry and the individual values of this dimensionfrom which its median is formed) may be in the same ratio relative tothe corresponding individual values of this dimension from which it isformed as L_(S) ^(i) to D_(S) ^(i) according to the present invention.

When reference is made in this document to the same geometries ofdifferent types of geometric shaped bodies, what is meant is that thedifferent types of geometric shaped bodies have essentially the samemedian geometry. In other words, the medians of mutually correspondingindividual dimensions of the shaped body geometries differ, based on thearithmetic mean of the two medians, by less than 10%, preferably by lessthan 5%. The individual dimensions of a median geometry may in principlehave the values recommended in the prior art for the correspondingdimension of an individual geometry.

A particularly preferred median ring geometry for multimetal oxide (I)shaped unsupported catalyst bodies is, for example, the geometryexternal diameter E 5 mm×length L 3 mm×internal diameter I 2 mm (whichis already recommended as a preferred individual geometry in the priorart).

Other favorable multimetal oxide (I) unsupported catalyst median ringgeometries E×L×I are the geometries 5 mm×2 mm×2 mm, or 5 mm×3 mm×3 mm,or 5.5 mm×3 mm×3.5 mm, or 6 mm×3 mm×4 mm, or 6.5 mm×3 mm×4.5 mm, or 7mm×3 mm×5 mm, or 7 mm×7 mm×3 mm, or 7 mm×7 mm×4 mm.

All of these multimetal oxide (I) unsupported catalyst median ringgeometries are suitable, for example, both for the catalytic partialoxidation of propylene to acrolein in the gas phase and for thecatalytic partial oxidation of isobutene or tert-butanol or the methylether of tert-butanol to methacrolein in the gas phase.

Regarding the active compositions of the stoichiometry of the generalformula I, the stoichiometric coefficient b is preferably from 2 to 4,the stoichiometric coefficient c preferably from 3 to 10, thestoichiometric coefficient d preferably from 0.02 to 2, thestoichiometric coefficient e preferably from 0 to 5 and thestoichiometric coefficient f advantageously from 0.5 or 1 to 10. Morepreferably, the aforementioned stoichiometric coefficients aresimultaneously within the preferred ranges mentioned.

Moreover, X¹ is preferably cobalt, X² is preferably K, Cs and/or Sr,more preferably K, X³ is preferably tungsten, zinc and/or phosphorus andX⁴ is preferably Si. More preferably, the variables X¹ to X⁴simultaneously have the aforementioned definitions.

The statements made regarding the median geometries of the shapedcatalyst bodies apply correspondingly to the shaped inert bodies. Theshaped inert bodies are preferably manufactured from C 220 steatite fromCeramTec.

Annular (spherical) shaped catalyst bodies are, appropriately from anapplication point of view, diluted with annular (spherical) shaped inertbodies in order to bring about an activity structuring of the catalystcharge in the catalyst tube. The annular shaped inert bodies preferablyhave the same median ring geometry as the annular shaped catalyst bodies(this statement also applies in the case of sphere geometry).

For a heterogeneously catalyzed partial gas phase oxidation to prepareacrolein or methacrolein, the catalyst charge in the catalyst tube withthe above-described annular shaped bodies is preferably eitherconfigured uniformly with only one inventive type S^(i) of unsupportedcatalyst rings for the entire length of the catalyst tube or structuredas follows.

Positioned at the catalyst tube inlet (in flow direction of the reactiongas mixture), for a length of from 10 to 60%, preferably from 10 to 50%,more preferably from 20 to 40% and most preferably from 25 to 35% (i.e.,for example, for a length of from 0.70 to 1.50 m, preferably from 0.90to 1.20 m), in each case of the total length of the catalytically activecatalyst charge in the catalyst tube, is a homogenized mixture of onlyone type S^(i) of the aforementioned annular unsupported catalysts andonly one type S^(i) of annular shaped inert bodies (both shaped bodytypes preferably have the same ring geometry), the proportion by weightof the shaped diluent bodies (the bulk densities of shaped catalystbodies and shaped diluent bodies generally differ only slightly) beingnormally from 5 to 40% by weight, or from 10 to 40% by weight, or from20 to 40% by weight, or from 25 to 35% by weight. Downstream of thisfirst charge section is then advantageously disposed, up to the end ofthe length of the catalyst charge (i.e., for example, for a length offrom 1.00 to 3.00 m or from 1.00 to 2.70 m, preferably from 1.40 to 3.00m or from 2.00 to 3.00 m), either a bed of the only one type S^(i) ofannular unsupported catalysts diluted only to a lesser extent (than inthe first section) with the only one type S^(i) of annular shaped inertbodies, or, most preferably, an exclusive (undiluted) bed of the sameonly one type S^(i) of annular unsupported catalyst. Of course, it isalso possible to select a uniform dilution over the entire catalyst tubelength. The fixed catalyst bed will be configured in a correspondingmanner when the geometries are spherical.

Otherwise, the heterogeneously catalyzed partial gas phase oxidation ofpropylene to acrolein or of isobutene to methacrolein can be performedin a tube bundle reactor having one or more temperature zones, asdescribed in the prior art (cf., for example, WO 2005/03093, DE-A 102007 005 602 and DE-A 10 2004 025 445, and the prior art cited in thesedocuments).

Useful active compositions for the geometric shaped catalyst bodies ofan inventive catalyst tube charge also include multielement oxides ofthe general formula IIMo₁₂P_(a)V_(b)X¹ _(c)X² _(d)X³ _(e)Sb_(f)Re_(g)S_(h)O_(n)  (II)where

-   X¹=potassium, rubidium and/or cesium,-   X²=copper and/or silver,-   X³=cerium, boron, zirconium, manganese and/or bismuth,-   a=0.5 to 3,-   b=0.01 to 3,-   c=0.2 to 3,-   d=0.01 to 2,-   e=0 to 2,-   f=0.01 to 2,-   g=0 to 1,-   h=0.001 to 0.5, and-   n=a number which is determined by the valency and frequency of the    elements in II other than oxygen.

Such geometric shaped catalyst bodies are suitable advantageouslyespecially for a heterogeneously catalyzed partial gas phase oxidationof methacrolein to methacrylic acid.

Aforementioned shaped catalyst bodies are preferably likewise annularunsupported catalysts, as obtainable, for example, by the proceduredescribed in EP-A 467 144. Useful median ring geometries are inparticular the individual geometries recommended in EP-A 467 144 andthose recommended with regard to the multielement oxides I in thisdocument. A preferred median ring geometry is that where E×L×I=7 mm×7mm×3 mm (cf. also DE-A 102007005602).

A structured dilution with annular shaped inert bodies can be effected,for example, as described for the case of the heterogeneously catalyzedpartial oxidation of propylene to acrolein. Otherwise, the partialoxidation process conditions described in EP-A 467 144 and DE-A 10 2007005 602 may be employed. For the heterogeneously catalyzed partial gasphase oxidation of hydrocarbons having at least four carbon atoms(especially n-butane, n-butenes and/or benzene) to maleic anhydride,useful multielement oxide active compositions for geometric shapedcatalyst bodies to be used in accordance with the invention areadvantageously those of the general formula II,V₁P_(b)Fe_(c)X¹ _(d)X² _(e)O_(n)  (III)in which the variables are each defined as follows:

-   X¹=Mo, Bi, Co, Ni, Si, Zn, Hf, Zr, Ti, Cr, Mn, Cu, B, Sn and/or Nb,-   X²=K, Na, Rb, Cs and/or TI,-   b=0.9 to 1.5,-   c=0 to 0.1,-   d=0 to 0.1,-   e=0 to 0.1, and-   n=a number which is determined by the valency and frequency of the    elements in III other than oxygen.

Advantageously, these shaped catalyst bodies are likewise annularunsupported catalysts, as obtainable, for example, according to WO03/078310, WO 01/68245, DE-A 10 2005 035 978 and DE-A 10 2007 005 602.Useful median ring geometries are in particular the individualgeometries recommended in the aforementioned documents and theindividual geometries recommended with regard to the multielement oxidesI in this document. A preferred median ring geometry is that whereE×L×I=5 mm×3.2 mm×2.5 mm (see also DE-A 10 2007 005 602).

A structured dilution with annular shaped inert bodies can be effected,for example, as described for the case of the heterogeneously catalyzedpartial oxidation of propylene to acrolein.

Otherwise, the partial oxidation process conditions recommended in WO03/078 310, WO 01/68245, DE-A 10 2005 035 978 and DE-A 10 2007 005 602can be applied.

For the heterogeneously catalyzed partial gas phase oxidation ofacrolein to acrylic acid, useful multielement oxide active compositionsfor geometric shaped catalyst bodies to be used in accordance with theinvention are advantageously those of the general formula IVMO₁₂V_(a)X¹ _(b)X² _(c)X³ _(d)X⁴ _(e)X⁵ _(f)X⁶ _(g)O_(n)  (IV)in which the variables are each defined as follows:

-   X¹=W, Nb, Ta, Cr and/or Ce,-   X²=Cu, Ni, Co, Fe, Mn and/or Zn,-   X³=Sb and/or Bi,-   X⁴=one or more alkali metals (Li, Na, K, Rb, Cs) and/or H,-   X⁵=one or more alkaline earth metals (Mg, Ca, Sr, Ba),-   X⁶=Si, Al, Ti and/or Zr,-   a=1 to 6,-   b=0.2 to 4,-   c=0 to 18, preferably 0.5 to 18,-   d=0 to 40,-   e=0 to 2,-   f=0 to 4,-   g=0 to 40, and-   n=a number which is determined by the valency and frequency of the    elements in IV other than oxygen.

Advantageously, these shaped catalyst bodies are annular or sphericalcoated catalysts, as obtainable, for example, according to DE-A 10 2004025 445, DE-A 10 350 822, DE-A 10 2007 010 422, US 2006/0205978 and EP-A714 700, and the prior art cited in these documents.

Useful median ring geometries or median sphere geometries are inparticular the individual geometries recommended in the aforementioneddocuments. A preferred median ring geometry is that where E×L×I=7 mm×3mm×4 mm for the parent annular shaped support bodies.

The active composition coating thickness may be from 10 to 1000 μm,preferably from 50 to 500 μm and more preferably from 150 to 250 μm.Favorable coating thicknesses are those of the exemplary embodiments ofEP-A 714 700.

For a heterogeneously catalyzed partial gas phase oxidation of acroleinto acrylic acid, the catalyst charge in the catalyst tube is preferablyeither configured uniformly with only one inventive type S^(i) of coatedcatalyst rings over the entire length of the catalyst tube or structuredas follows.

Positioned at the catalyst tube inlet (in flow direction of the reactiongas mixture), for a length of from 10 to 60%, preferably from 10 to 50%,more preferably from 20 to 40% and most preferably from 25 to 35% (i.e.,for example, for a length of from 0.70 to 1.50 m, preferably from 0.90to 1.20 m), in each case of the total length of the catalytically activecatalyst charge in the catalyst tube, is a homogenized mixture composedof only one type S^(i) of the abovementioned annular coated catalystsand only one type S^(i) of annular shaped inert bodies (both shaped bodytypes preferably have the same ring geometry), the proportion by weightof the shaped diluent bodies (the bulk densities of shaped catalystbodies and of shaped diluent bodies generally differ only slightly)being normally from 5 to 40% by weight, or from 10 to 40% by weight, orfrom 20 to 40% by weight, or from 25 to 35% by weight. Downstream ofthis first charge section is then advantageously disposed, up to the endof the length of the catalyst charge (i.e., for example, for a length offrom 2.00 to 3.00 m, preferably from 2.50 to 3.00 m), either a bed ofthe only one type S^(i) of annular unsupported catalysts diluted only toa lesser extent (than in the first section) with the only one type S^(i)of annular shaped inert bodies, or, most preferably, an exclusive(undiluted) bed of the same only one type S^(i) of annular coatedcatalyst. The fixed catalyst bed will be configured in a correspondingmanner when the coated catalyst geometry is spherical.

Otherwise, the heterogeneously catalyzed gas phase oxidation of acroleinto acrylic acid can be performed in a tube bundle reactor having one ormore temperature zones as described in the prior art (cf., for example,DE-A 10 2004 025 445, DE-A 10 350 822, DE-A 10 2007 010 422, US2006/0205978 and EP-A 714 700, and the prior art cited in thesedocuments).

A multielement oxide comprising V and Sb (especially one according tothe documents U.S. Pat. Nos. 6,528,683, 6,586,361, or U.S. Pat. No.6,362,345) is suitable especially for a heterogeneously catalyzedpartial oxidation of o-xylene and/or naphthalene to phthalic anhydride.

In this case, preference is given to using the aforementionedmultielement oxides as annular or as spherical coated catalysts. Usefulsupport bodies are in particular those which consist to an extent of atleast 80% by weight of titanium dioxide. Exemplary median ringgeometries include the ring geometries E×L×I=8 mm×6 mm×5 mm, or 8 mm×6mm×4 mm, or 8 mm×6 mm×3 mm and 7 mm×7 mm×4 mm.

Shaped catalyst bodies whose active composition comprises elementalsilver on an oxidic support body are suitable (in particular assupported catalysts) especially for a heterogeneously catalyzed partialgas phase oxidation of ethylene to ethylene oxide (cf. EP-A 496-470).

In this case, the shaped catalyst body geometry may likewise bespherical or annular. Useful shaped support bodies are in particularthose which consist to an extent of at least 80% by weight of aluminumoxide (e.g. Al₂O₃).

Exemplary median sphere geometries here include the sphere diameters 4mm, 5 mm and 7 mm.

Quite generally, in the processes described for heterogeneouslycatalyzed partial gas phase oxidation, a pure shaped inert body bedwhose length, based on the total length of the fixed catalyst bed,within the catalyst tube is appropriately from 1 or 5 to 20% canintroduce the fixed catalyst bed in flow direction of the reaction gas.It is normally utilized as a heating zone for the reaction gas mixture.

Generally, it is advantageous in the process according to the inventionwhen the median D_(S) ^(i) of the longest dimension L_(S) ^(i) of onetype S^(i) used in the catalyst tube to charge a fixed catalyst bedsection has the following ratio relative to the internal diameter R ofthe catalyst tube: R/D_(S) ^(i)=from 1.5 to 5, preferably from 2 to 4and more preferably from 3 to 3.5.

Moreover, it is advantageous for the process according to the inventionwhen the arithmetic mean M_(S) ^(i) of the longest dimensions L_(S) ^(i)which form the basis of the median D_(S) ^(i) deviates from D_(S) ^(i)by not more than 10%, preferably not more than 5% (with D_(S) ^(i) asthe reference basis). All statements in this document apply especiallywhen the geometric shaped catalyst bodies and the geometric shaped inertbodies are rings. The catalyst tubes can otherwise generally be filledas described in WO 2006/094 766 and WO 2005/113 123 and JP-A 2004 195279.

All statements made in this document also apply especially to the coatedcatalysts having a multielement oxide active composition comprising Moand V from documents EP-A 1 254 707, EP-A 1 254 710, EP-A 1 254 709, WO2004/035528, DE-A 102 48 584, DE-A 102 54 278, DE-A 102 54 279, WO02/06199 and WO 02/051539, and to the partial oxidations, catalyzed bythese coated catalysts, of propane to acrolein and/or acrylic acid, andof isobutane to methacrolein and/or methacrylic acid.

In addition, all statements made in this document also apply especiallyto the coated catalysts having a multielement oxide active compositioncomprising Mo and V from DE-A 10 2007 010 422, and to the partialoxidations catalyzed by these coated catalysts (especially of acroleinto acrylic acid).

The present invention thus comprises especially the followingembodiments:

-   1. A process for charging a longitudinal section of a catalyst tube    with a uniform fixed catalyst bed section whose active composition    is at least one multielement oxide which comprises    -   a) the elements Mo, Fe and Bi, or    -   b) the elements Mo and V, or    -   c) the element V and additionally P and/or Sb,    -   or whose active composition comprises elemental silver on an        oxidic support body, and which consists of a single type S^(i)        or of a homogenized mixture of a plurality of mutually        distinguishable types S^(i) of geometric shaped catalyst bodies        or of geometric shaped catalyst bodies and geometric shaped        inert bodies, where the median of the longest dimensions L_(S)        ^(i) of the geometric shaped bodies of one type S^(i) has a        value D_(S) ^(i), wherein, at least within one type S^(i) of        geometric shaped bodies, the proviso M that

from 40 of the total number of geometric shaped bodies belonging to to70% S^(i) has a longest dimension L_(S) ^(i) for which 0.98 · D_(S) ^(i)≦ L_(S) ^(i) ≦ 1.02 · D_(S) ^(i), at least 10% of the total number ofthe geometric shaped bodies belonging to S^(i) has a longest dimensionL_(S) ^(i) for which 0.94 · D_(S) ^(i) ≦ L_(S) ^(i) < 0.98 · D_(S) ^(i),at least 10% of the total number of the geometric shaped bodiesbelonging to S^(i) has a longest dimension L_(S) ^(i) for which 1.02 ·D_(S) ^(i) < L_(S) ^(i) ≦ 1.10 · D_(S) ^(i), less than 5% of the totalnumber of geometric shaped bodies belonging to S^(i) has a longestdimension L_(S) ^(i) for which 0.94 · D_(S) ^(i) > L_(S) ^(i), and lessthan 5% of the total number of the geometric shaped bodies belonging toS^(i) has a longest dimension L_(S) ^(i) for which 1.10 · D_(S) ^(i) <L_(S) ^(i)is satisfied.

-   2. A process according to embodiment 1, wherein, at least within one    type S^(i) of geometric shaped bodies, the proviso M* that

from 50 of the total number of geometric shaped bodies belonging to to60% S^(i) has a longest dimension L_(S) ^(i) for which 0.98 · D_(S) ^(i)≦ L_(S) ^(i) ≦ 1.02 · D_(S) ^(i), at least 15% of the total number ofthe geometric shaped bodies belonging to S^(i) has a longest dimensionL_(S) ^(i) for which 0.94 · D_(S) ^(i) ≦ L_(S) ^(i) < 0.98 · D_(S) ^(i),at least 15% of the total number of the geometric shaped bodiesbelonging to S^(i) has a longest dimension L_(S) ^(i) for which 1.02 ·D_(S) ^(i) < L_(S) ^(i) ≦ 1.10 · D_(S) ^(i), less than 5% of the totalnumber of geometric shaped bodies belonging to S^(i) has a longestdimension L_(S) ^(i) for which 0.94 · D_(S) ^(i) > L_(S) ^(i), and lessthan 5% of the total number of the geometric shaped bodies belonging toS^(i) has a longest dimension L_(S) ^(i) for which 1.10 · D_(S) ^(i) <L_(S) ^(i)is satisfied.

-   3. A process according to embodiment 1, wherein, at least within one    type S^(i) of geometric shaped bodies, the proviso M** that

from 50 of the total number of geometric shaped bodies belonging to to60% S^(i) has a longest dimension L_(S) ^(i) for which 0.98 · D_(S) ^(i)≦ L_(S) ^(i) ≦ 1.02 · D_(S) ^(i), at least 20% of the total number ofthe geometric shaped bodies belonging to S^(i) has a longest dimensionL_(S) ^(i) for which 0.94 · D_(S) ^(i) ≦ L_(S) ^(i) < 0.98 · D_(S) ^(i),at least 20% of the total number of the geometric shaped bodiesbelonging to S^(i) has a longest dimension L_(S) ^(i) for which 1.02 ·D_(S) ^(i) < L_(S) ^(i) ≦ 1.10 · D_(S) ^(i), less than 5% of the totalnumber of geometric shaped bodies belonging to S^(i) has a longestdimension L_(S) ^(i) for which 0.94 · D_(S) ^(i) > L_(S) ^(i), and lessthan 5% of the total number of the geometric shaped bodies belonging toS^(i) has a longest dimension L_(S) ^(i) for which 1.10 · D_(S) ^(i) <L_(S) ^(i)is satisfied.

-   4. A process according to any of embodiments 1 to 3, wherein the    fixed catalyst bed section consists of only a single type S^(i) of    annular or of spherical shaped catalyst bodies.-   5. A process according to embodiment 1, wherein the shaped catalyst    bed section consists of a homogenized mixture of only one type of    annular shaped catalyst bodies and only one type of annular shaped    inert bodies, wherein both the only one type of annular shaped    catalyst bodies and the only one type of annular shaped inert bodies    satisfy the proviso M.-   6. A process according to embodiment 2, wherein the shaped catalyst    bed section consists of a homogenized mixture of only one type of    annular shaped catalyst bodies and only one type of annular shaped    inert bodies, wherein both the only one type of annular shaped    catalyst bodies and the only one type of annular shaped inert bodies    satisfy the proviso M*.-   7. A process according to embodiment 3, wherein the shaped catalyst    bed section consists of a homogenized mixture of only one type of    annular shaped catalyst bodies and only one type of annular shaped    inert bodies, wherein both the only one type of annular shaped    catalyst bodies and the only one type of annular shaped inert bodies    satisfy the proviso M**.-   8. A process for charging a catalyst tube with a fixed catalyst bed    which consists of a plurality of successive and mutually different    catalytically active fixed catalyst bed sections, each of which is    intrinsically homogeneous, and where the active composition of all    fixed catalyst bed sections comprises at least one multielement    oxide which comprises    -   a) the elements Mo, Fe and Bi, or    -   b) the elements Mo and V, or    -   c) the element V and additionally P and/or Sb,    -   or whose active composition comprises elemental silver on an        oxidic support body, and the individual fixed catalyst bed        section consists of a single type S^(i) or of a homogenized        mixture of a plurality of mutually distinguishable types S^(i)        of geometric shaped catalyst bodies and geometric shaped inert        bodies, wherein, in each individual fixed catalyst bed section,        all types S^(i) of geometric shaped bodies present therein in        each case satisfy the proviso M according to embodiment 1, or        the proviso M* according to embodiment 2, or the proviso M**        according to embodiment 3.-   9. A process according to embodiment 8, wherein all geometric shaped    bodies are rings or spheres.-   10. A process according to embodiment 9, wherein all geometric    shaped bodies have the same ring geometry or the same sphere    geometry.-   11. A process according to embodiment 10, wherein the combined    medium D^(inert) _(cat), formed over the total number G of all    longest dimensions L_(cat) of the geometric shaped catalyst bodies    and all longest dimensions L_(inert) of the geometric shaped inert    bodies, and the longest dimensions L_(inert) and L_(cat) (i.e.    L_(cat,inert)) satisfy the proviso M^(G)* that

from 40 to 70% of the total number G has a longest dimensionL_(cat,inert) for which 0.98 · D^(inert) _(cat) ≦ L_(cat,inert) ≦ 1.02 ·D^(inert) _(cat), at least 10% of the total number G has a longestdimension L_(cat,inert) for which 0.94 · D^(inert) _(cat) ≦L_(cat,inert) < 0.98 · D^(inert) _(cat), at least 10% of the totalnumber G has a longest dimension L_(cat,inert) for which 1.02 ·D^(inert) _(cat) < L_(cat,inert) ≦ 1.10 · D^(inert) _(cat), less than 5%of the total number G has a longest dimension L_(cat,inert) for which0.94 · D^(inert) _(cat) > L_(cat,inert,) and less than 5% of the totalnumber G has a longest dimension L_(cat,inert) for which 1.10 ·D^(inert) _(cat) < L_(cat,inert)is satisfied.

-   12. A process according to embodiment 11, wherein the entire fixed    catalyst bed comprises only one type of annular shaped catalyst    bodies and only one type of annular shaped inert bodies or only one    type of spherical shaped catalyst bodies and only one type of    spherical shaped inert bodies.-   13. A process according to any of embodiments 5 to 7, wherein the    shaped catalyst bodies and the shaped inert bodies are not annular    but spherical.-   14. A tube bundle reactor comprising at least one catalyst tube    which has been charged by a process according to any of embodiments    1 to 13.-   15. A process for heterogeneously catalyzed partial gas phase    oxidation of an organic compound in a tube bundle reactor, wherein    the tube bundle reactor is a tube bundle reactor according to    embodiment 14.-   16. A process according to embodiment 15, wherein the    heterogeneously catalyzed partial gas phase oxidation is that of    propylene to acrolein and/or that of acrolein to acrylic acid.-   17. A process for preparing organic compounds (e.g. all of those    mentioned in this document, for example acrolein, acrylic acid,    methacrylic acid, maleic anhydride, ethylene oxide and phthalic    anhydride), which comprises a process according to any of    embodiments 1 to 12.

Otherwise, all data in this document, unless explicitly statedotherwise, are based on a temperature of 25° C. and a pressure of 1 atm.

EXAMPLE AND COMPARATIVE EXAMPLES Comparative Example 1

Like the unsupported catalyst BVK 3 in WO 2005/030 393, using TIMREX T44 from Timcal AG (Bodio, Switzerland) as auxiliary graphite, one typeof annular unsupported catalysts of stoichiometry (without takingaccount of graphite still present)Mo₁₂Bi₁W₂Co_(5.5)Fe_(2.94)Si_(1.59)K_(0.08)O_(x)was prepared.

The median geometry of the annular unsupported catalysts was E×L×I=5mm×3 mm×2 mm.

Between the median of its longest dimension D_(S) ^(i) (5.83 mm) and theindividual longest dimensions L_(S) ^(i), the following condition wassatisfied:0.99·5.83 mm≦L_(S) ^(i)≦1.01·5.83 mm.

A catalyst tube (V2A steel; external diameter 21 mm, wall thickness 3mm, internal diameter 15 mm, length 100 cm) was charged using steatiteshaped inert body rings of the same annular median geometry in flowdirection of the later reaction gas as follows:

-   Section 1: length 30 cm, bed only of the inert shaped body rings;-   Section 2: length 70 cm, bed only of the annular unsupported    catalysts.

The catalyst tube was heated by means of a nitrogen-sparged salt bath.

The catalyst tube was charged with a charge gas mixture (mixture of air,polymer-grade propylene and nitrogen) of the following composition:

-   -   5% by volume of propylene,    -   10% by volume of molecular oxygen, and    -   as the remainder to 100% by volume, N₂.

The propylene loading of the fixed catalyst bed was selected at 50 I(STP)/(I·h). The salt bath temperature was adjusted such that thepropylene conversion, based on a single pass of the reaction gas mixturethrough the catalyst tube, was 95 mol %.

The selectivity of the resulting product of value formation of acroleinand acrylic acid was 95.7 mol %.

Comparative Example 2

The procedure was as in Comparative example 1. To charge section 2 ofthe catalyst tube, however, a homogenized mixture of annular unsupportedcatalysts of the same median geometry and active composition was used,except that the following relationships were satisfied between themedian of the longest dimensions and the individual longest dimensions:

For 80% of the rings: 0.98·5.83 mm≦L_(S) ^(i)≦1.02·5.83 mm.

For 20% of the rings: 1.02·5.83 mm<L_(S) ^(i)≦1.10·5.83 mm.

The selectivity of the resulting product of value formation of acroleinand acrylic acid was, under otherwise identical operating conditions,95.8 mol %.

Example

The procedure was as in Comparative example 1. To charge section 2 ofthe catalyst tube, however, a homogenized mixture of annular unsupportedcatalysts of the same median geometry and active composition was used,except that the following relationships were satisfied between themedian of the longest dimensions and the individual longest dimensions:

For 60% of the rings: 0.98·5.73 mm≦L_(S) ^(i)≦1.02·5.73 mm.

For 20% of the rings: 0.94·5.73 mm≦L_(S) ^(i)<0.98·5.73 mm.

For 20% of the rings: 1.02·5.73 mm<L_(S) ^(i)≦1.10·5.73 mm.

The selectivity of the resulting product of value formation of acroleinand acrylic acid was, under otherwise identical operating conditions,96.2 mol %.

U.S. Provisional Patent Application No. 60/910,908, filed Apr. 10, 2007,is incorporated into the present patent application by literaturereference. With regard to the abovementioned teachings, numerous changesand deviations from the present invention are possible.

It can therefore be assumed that the invention, within the scope of theappended claims, can be performed differently from the way describedspecifically herein.

The invention claimed is:
 1. A process for charging a longitudinalsection of a catalyst tube with a uniform fixed catalyst bed sectionwhose active composition is at least one multielement oxide whichcomprises a) the elements Mo, Fe and Bi, or b) the elements Mo and V, orc) the element V and additionally P and/or Sb, or whose activecomposition comprises elemental silver on an oxidic support body, andwhich consists of a single type S^(i) or of a homogenized mixture of aplurality of mutually distinguishable types S^(i) of geometric shapedcatalyst bodies or of geometric shaped catalyst bodies and geometricshaped inert bodies, where the median of the longest dimensions L_(s)^(i) of the geometric shaped bodies of one type S^(i) has a value D_(s)^(i), wherein, at least within one type S^(i) of geometric shapedbodies, the proviso M that from 40 of the total number of geometricshaped bodies belonging to to 70% S^(i) has a longest dimension L_(S)^(i) for which 0.98 · D_(S) ^(i) ≦ L_(S) ^(i) ≦ 1.02 · D_(S) ^(i), atleast 10% of the total number of the geometric shaped bodies belongingto S^(i) has a longest dimension L_(S) ^(i) for which 0.94 · D_(S) ^(i)≦ L_(S) ^(i) < 0.98 · D_(S) ^(i), at least 10% of the total number ofthe geometric shaped bodies belonging to S^(i) has a longest dimensionL_(S) ^(i) for which 1.02 · D_(S) ^(i) < L_(S) ^(i) ≦ 1.10 · D_(S) ^(i),less than 5% of the total number of geometric shaped bodies belonging toS^(i) has a longest dimension L_(S) ^(i) for which 0.94 · D_(S) ^(i) >L_(S) ^(i), and less than 5% of the total number of the geometric shapedbodies belonging to S^(i) has a longest dimension L_(S) ^(i) for which1.10 · D_(S) ^(i) < L_(S) ^(i)

is satisfied.
 2. The process according to claim 1, wherein, at leastwithin one type S^(i) of geometric shaped bodies, the proviso M^(*) thatfrom 50 of the total number of geometric shaped bodies belonging to to60% S^(i) has a longest dimension L_(S) ^(i) for which 0.98 · D_(S) ^(i)≦ L_(S) ^(i) ≦ 1.02 · D_(S) ^(i), at least 15% of the total number ofthe geometric shaped bodies belonging to S^(i) has a longest dimensionL_(S) ^(i) for which 0.94 · D_(S) ^(i) ≦ L_(S) ^(i) < 0.98 · D_(S) ^(i),at least 15% of the total number of the geometric shaped bodiesbelonging to S^(i) has a longest dimension L_(S) ^(i) for which 1.02 ·D_(S) ^(i) < L_(S) ^(i) ≦ 1.10 · D_(S) ^(i), less than 5% of the totalnumber of geometric shaped bodies belonging to S^(i) has a longestdimension L_(S) ^(i) for which 0.94 · D_(S) ^(i) > L_(S) ^(i), and lessthan 5% of the total number of the geometric shaped bodies belonging toS^(i) has a longest dimension L_(S) ^(i) for which 1.10 · D_(S) ^(i) <L_(S) ^(i)

is satisfied.
 3. The process according to claim 1, wherein, at leastwithin one type S^(i) of geometric shaped bodies, the proviso M^(**)that from 50 of the total number of geometric shaped bodies belonging toto 60% S^(i) has a longest dimension L_(S) ^(i) for which 0.98 · D_(S)^(i) ≦ L_(S) ^(i) ≦ 1.02 · D_(S) ^(i), at least 20% of the total numberof the geometric shaped bodies belonging to S^(i) has a longestdimension L_(S) ^(i) for which 0.94 · D_(S) ^(i) ≦ L_(S) ^(i) < 0.98 ·D_(S) ^(i), at least 20% of the total number of the geometric shapedbodies belonging to S^(i) has a longest dimension L_(S) ^(i) for which1.02 · D_(S) ^(i) < L_(S) ^(i) ≦ 1.10 · D_(S) ^(i), less than 5% of thetotal number of geometric shaped bodies belonging to S^(i) has a longestdimension L_(S) ^(i) for which 0.94 · D_(S) ^(i) > L_(S) ^(i), and lessthan 5% of the total number of the geometric shaped bodies belonging toS^(i) has a longest dimension L_(S) ^(i) for which 1.10 · D_(S) ^(i) <L_(S) ^(i)

is satisfied.
 4. The process according to claim 1, wherein the fixedcatalyst bed section consists of only a single type S^(i) of annular orof spherical shaped catalyst bodies.
 5. The process according to claim1, wherein the shaped catalyst bed section consists of a homogenizedmixture of only one type of annular shaped catalyst bodies and only ofone type of annular shaped inert bodies, wherein both the only one typeof annular shaped catalyst bodies and the only one type of annularshaped inert bodies satisfy the proviso M.
 6. The process according toclaim 2, wherein the shaped catalyst bed section consists of ahomogenized mixture of only one type of annular shaped catalyst bodiesand only one type of annular shaped inert bodies, wherein both the onlyone type of annular shaped catalyst bodies and the only one type ofannular shaped inert bodies satisfy the proviso M^(*).
 7. The processaccording to claim 3, wherein the shaped catalyst bed section consistsof a homogenized mixture of only one type of annular shaped catalystbodies and only one type of annular shaped inert bodies, wherein boththe only one type of annular shaped catalyst bodies and the only onetype of annular shaped inert bodies satisfy the proviso M^(**).
 8. Aprocess for charging a catalyst tube with a fixed catalyst bed whichconsists of a plurality of successive and mutually differentcatalytically active fixed catalyst bed sections, each of which isintrinsically homogeneous, and where the active composition of all fixedcatalyst bed sections comprises at least one multielement oxide whichcomprises a) the elements Mo, Fe and Bi, or b) the elements Mo and V, orc) the element V and additionally P and/or Sb, or whose activecomposition comprises elemental silver on an oxidic support body, andthe individual fixed catalyst bed section consists of a single typeS^(i) or of a homogenized mixture of a plurality of mutuallydistinguishable types S^(i) of geometric shaped catalyst bodies andgeometric shaped inert bodies, wherein, in each individual fixedcatalyst bed section, all types S^(i) of geometric shaped bodies presenttherein in each case satisfy the proviso M according to claim
 1. 9. Theprocess according to claim 8, wherein all geometric shaped bodies arerings or spheres.
 10. The process according to claim 9, wherein allgeometric shaped bodies have the same ring geometry or the same spheregeometry.
 11. The process according to claim 10, wherein a combinedmedium D^(inert) _(cat,)formed over a total number G of all longestdimensions L_(cat) of the geometric shaped catalyst bodies and alllongest dimensions L_(inert) of the geometric shaped inert bodies, andthe longest dimensions L_(inert) and L_(cat) represented by theL_(cat,inert) satisfy the proviso M^(G*) that from 40 to 70% of thetotal number G has a longest dimension L_(cat,inert) for which 0.98 ·D^(inert) _(cat) ≦ L_(cat,inert) ≦ 1.02 · D^(inert) _(cat), at least 10%of the total number G has a longest dimension L_(cat,inert) for which0.94 · D^(inert) _(cat) ≦ L_(cat,inert) < 0.98 · D^(inert) _(cat), atleast 10% of the total number G has a longest dimension L_(cat,inert)for which 1.02 · D^(inert) _(cat) < L_(cat,inert) ≦ 1.10 · D^(inert)_(cat), less than 5% of the total number G has a longest dimensionL_(cat,inert) for which 0.94 · D^(inert) _(cat) > L_(cat,inert), andless than 5% of the total number G has a longest dimension L_(cat,inert)for which 1.10 · D^(inert) _(cat) < L_(cat,inert).


12. The process according to claim 11, wherein the entire fixed catalystbed comprises only one type of annular shaped catalyst bodies and onlyone type of annular shaped inert bodies or only one type of sphericalshaped catalyst bodies and only one type of spherical shaped inertbodies.
 13. The process according to claim 5, wherein the shapedcatalyst bodies and the shaped inert bodies are not annular butspherical.
 14. A process for preparing acrolein, acrylic acid,methacrylic acid, maleic anhydride, ethylene oxide or phthalicanhydride, which comprises a process according to claim
 1. 15. Theprocess according to claim 2, wherein the fixed catalyst bed sectionconsists of only a single type S^(i) of annular or of spherical shapedcatalyst bodies.
 16. The process according to claim 3, wherein the fixedcatalyst bed section consists of only a single type S^(i) of annular orof spherical shaped catalyst bodies.
 17. The process according to claim8, wherein, in each individual fixed catalyst bed section, all typesS^(i) of geometric shaped bodies present therein in each case satisfythe proviso: from 50 to 60% of the total number of geometric shapedbodies belonging to S^(i) has a longest dimension L_(S) ^(i) for which0.98 · D_(S) ^(i) ≦ L_(S) ^(i) ≦ 1.02 · D_(S) ^(i), at least 15% of thetotal number of the geometric shaped bodies belonging to S^(i) has alongest dimension L_(S) ^(i) for which 0.94 · D_(S) ^(i) ≦ L_(S) ^(i) <0.98 · D_(S) ^(i), at least 15% of the total number of the geometricshaped bodies belonging to S^(i) has a longest dimension L_(S) ^(i) forwhich 1.02 · D_(S) ^(i) < L_(S) ^(i) ≦ 1.10 · D_(S) ^(i), less than 5%of the total number of geometric shaped bodies belonging to S^(i) has alongest dimension L_(S) ^(i) for which 0.94 · D_(S) ^(i) > L_(S) ^(i),and less than 5% of the total number of the geometric shaped bodiesbelonging to S^(i) has a longest dimension L_(S) ^(i) for which 1.10 ·D_(S) ^(i) < L_(S) ^(i).


18. The process according to claim 8, wherein, in each individual fixedcatalyst bed section, all types S^(i) of geometric shaped bodies presenttherein in each case satisfy the proviso: from 50 to 60% of the totalnumber of geometric shaped bodies belonging to S^(i) has a longestdimension L_(S) ^(i) for which 0.98 · D_(S) ^(i) ≦ L_(S) ^(i) ≦ 1.02 ·D_(S) ^(i), at least 20% of the total number of the geometric shapedbodies belonging to S^(i) has a longest dimension L_(S) ^(i) for which0.94 · D_(S) ^(i) ≦ L_(S) ^(i) < 0.98 · D_(S) ^(i), at least 20% of thetotal number of the geometric shaped bodies belonging to S^(i) has alongest dimension L_(S) ^(i) for which 1.02 · D_(S) ^(i) < L_(S) ^(i) ≦1.10 · D_(S) ^(i), less than 5% of the total number of geometric shapedbodies belonging to S^(i) has a longest dimension L_(S) ^(i) for which0.94 · D_(S) ^(i) > L_(S) ^(i), and less than 5% of the total number ofthe geometric shaped bodies belonging to S^(i) has a longest dimensionL_(S) ^(i) for which 1.10 · D_(S) ^(i) < L_(S) ^(i).


19. The process according to claim 6, wherein the shaped catalyst bodiesand the shaped inert bodies are not annular but spherical.
 20. Theprocess according to claim 7, wherein the shaped catalyst bodies and theshaped inert bodies are not annular but spherical.
 21. A process forpreparing acrolein, acrylic acid, methacrylic acid, maleic anhydride,ethylene oxide or phthalic anhydride, which comprises a processaccording to claim 8.